The present invention relates to a method for mounting components, such as electronic components, onto a circuit substrate, such as an electronic circuit board, as well as an apparatus for mounting components which is capable of performing such a method. The present invention also relates to a computer readable storage medium for performing such a method.
In the field of component mounting for mounting components, such as electronic components, onto a circuit substrate, such as an electronic circuit board, a plurality of supplying devices carrying numbers of components are attached to a component mounting apparatus, and the components are picked up one after another from these supplying devices in a predetermined order. Each component is then detected as to whether it is held by a component holder in a proper condition for mounting. If it is determined that the component is held in a proper condition, a displacement amount between the component and the component holder is measured. After necessary positional correction is made based on this measured displacement, the component is mounted on a predetermined position of a circuit substrate. If it is determined that the component is held in an improper condition for mounting, or the component is held in a position where proper imaging may not be performed by an imaging device, the component holder does not mount such a component onto a circuit substrate, but rather releases the component at a predetermined station.
The term “circuit substrate” used hereinafter means a material on which electronic components may be mounted. An electronic circuit board is a typical example of the circuit substrate. In these days, however, there are some cases where components are mounted on other types of materials, such as a casing of electronic equipment. Therefore, the term “circuit substrate” used in this specification includes any other types of materials onto which components may be mounted.
Based on a market demand for smaller and lighter electronic devices in recent years, density of components mounted on a circuit substrate has become higher, and hence a space between the components mounted adjacently becomes narrower, and a size of a component itself becomes smaller. For a purpose avoiding any damage to adjacent components already mounted on a circuit substrate, more severe control of a holding condition of a component by the component holder is required. Further, a tip of a nozzle, or a component holder, for sucking a component tends to be designed as small as possible so as not to interfere with a component already mounted, when the nozzle approaches the circuit substrate for mounting a subsequent component.
A conventional component mounting apparatus is now described by referring to FIGS. 5 to 7. FIG. 5 shows an overall view of the component mounting apparatus. Referring to FIG. 5, the component mounting apparatus includes a main body 1 and a component supply 2. A series of component mounting operations are performed inside the main body 1, which includes picking up a component supplied to the component supply 2, and mounting the component onto a circuit substrate supplied from one side of the main body 1.
FIGS. 6(A) and 6(B) show perspective views of a reel carrying numbers of components, and a cassette or a supplying device, respectively, used for supplying components to the component supply 2. In FIG. 6(A), numbers of components 3 are contained in a tape 4 by having a definite space 5 between adjacent components, and the tape 4 is wound on a reel 6. The reel 6 is then rotatably attached to the component supply device, or a cassette 7 as shown in FIG. 6(B). The cassette 7 moves forward the tape 4 intermittently for a distance equivalent to the space 5 so that the components 3 are placed at a component pick up window 9 one after another. Normally, a plurality of cassettes 7 are attached to the component supply 2 of the component mounting apparatus, as seen in FIG. 5. The component supply 2 is driven back and forth in an X direction shown in FIG. 5 by a motor, so that the cassette 7 carrying the components to be picked up may be positioned at the predetermined picking up station. Although a cassette type of the component supply device is illustrated in FIGS. 6(A) and 6(B), some other types, such as a bulk feeder type to supply components using compressed air, or a tray type to supply components by arranging components on a flat tray, may be used.
FIG. 7 schematically shows a series of component mounting operations, from picking up a component to mounting the same onto a circuit substrate, all of which are performed inside the main body 1 of the component mounting apparatus shown in FIG. 5. The cassette 7, or a supplying device, is attached to the component supply 2 at the right hand side of a Y direction of FIG. 7. As described above, components 3 are supplied one by one from the reel 6 attached to the cassette 7 to the pick up window 9 by an operation of a lever 8. On another side of the Y direction of the drawing, an element 10 is located inside the main body 1. As a main portion of the element 10, an index 11 holds a plurality of placement heads 12 on its circumference, which are used for mounting components onto a circuit substrate. As the index 11 is rotated intermittently in a direction shown by an arrow 13 by virtue of a motor, each placement head 12 is rotated and shifted in its position sequentially. A nozzle 14, or a component holder, is capable of moving up and down in a Z direction of the drawing, and is capable of rotating around a central axis parallel to a Z axis of the drawing, each of which is driven by a motor. Piping is connected to each nozzle to supply a vacuum and compressed air for sucking and releasing a component. A circuit substrate 21 is supplied to the main body 1 by a feeder, and held firmly by a circuit substrate holder, not shown in the drawing, and is capable of moving both in X and Y directions of the drawing by virtue of motors.
Again referring to FIG. 7, a nozzle 14 positioned at pick up station 15 sucks a component 3 from the pick up window 9 of the cassette 7 by virtue of a vacuum. The nozzle 14 then moves next to detecting station 16 by a next intermittent rotation of the index 11, where a holding condition of the component 3 is detected by a condition sensor 17. When the index 11 rotates further, the nozzle 14 moves next to imaging station 18, where a sucking point of the component 3 is recognized by an imaging device 19. With a further intermittent rotation of the index 11, the nozzle 14 is moved to mounting station 20 where the nozzle 14 moves down in the Z direction of the drawing, and mounts the component 3 on the predetermined mounting position of the circuit substrate 21. The circuit substrate 21 may be moved by the circuit substrate holder in both X and Y directions in accordance with predetermined mounting positional data (by virtue of an NC program).
When the condition sensor 17 determines that the component 3 is not in a proper condition for mounting, the nozzle 14 does not mount such a component 3 at mounting station 20, but rather, releases it into a collecting box 23 when the nozzle 14 moves next to releasing station 22. Each of the plurality of nozzles 14 attached to each placement head 12 performs operations of sucking, mounting, and, if necessary, releasing component 3 synchronously in accordance with intermittent rotation of the index 11. Reference numerals 26 and 25 in FIG. 7 are a controller for determining a component holding condition, and a controller for recognizing a component sucking point and measuring displacement, respectively. In FIG. 7, components 3 shown at and after the detecting station 16 are illustrated somewhat oversized for a purpose of easier understanding.
Next, an outline of a method for determining a holding condition of a component is described by referring to FIG. 8. A holding condition of component 3 sucked by nozzle 14 is detected, for example, by a line sensor 17 projecting beams from a projection side 28 toward a receiving side 29. As shown in this figure, if a height of the component 3 held by the nozzle 14 falls within a predetermined allowance Δh compared to a targeted height h1 (h1=nozzle height h2−thickness of the component 3), in other words, if the relation(h1−Δh)<h1<(h1+Δh)is satisfied, it is determined that the nozzle 14 holds a correct component 3 intended to be picked up, and that the component 3 is in proper condition for mounting. To the contrary, if detected height h3 satisfies the relationship,h3<(h1−Δh)it is determined that component 3 is not in proper condition for mounting (hereinafter, referred to as “an improperly held condition”). If it is determined that the component 3 is in an improperly held condition, that particular component 3 would not be mounted at mounting station 20 of FIG. 7, but rather, the component 3 is released into the collecting box 23 at the releasing station 22. If the nozzle 14 sucks a false component, or a component which is not intended to be picked up, such a false component is detected in a similar manner, and such a false component is also released into the collecting box 23 at the releasing station 22.
FIG. 9 shows a method for measuring a displacement value between a sucking point 31 of the component 3 and a position of the nozzle 14, which is performed at imaging station 18. In this figure, a rectangle in solid lines shows a configuration of a sucked component 3, while a dotted circular line shows the nozzle 14 sucking the component 3. A targeted sucking point of the component 3 may be predetermined based on, for example, a configuration or a center of gravity of the component 3. To make understanding easier, the targeted sucking point in FIG. 9 is located at a center 31 of the component 3. The sucking point of the nozzle 14 may also be predetermined on a nozzle by nozzle basis, but in this case, too, the sucking point is located at a center 32 of the nozzle 14 for easier understanding. The imaging device 19 provided at the imaging station 18 of the index 11 rotation shown in FIG. 7 images the component 3 sucked by the nozzle 14 from its bottom, and recognizes the center 31 of the component 3 as shown in FIG. 9. Since the center 32 of the nozzle 14 is previously known, displacement values in X direction (Δx) and Y direction (Δy) between the center 32 of the nozzle 14 and the center 31 of the component 3 are measured, whereby a total displacement value Δa may be measured.
Tilt angle of the component 3 held by the nozzle 14 is also recognized at imaging station 18. For example, if the component 3 is tilted against X and Y axes of the drawing, such tilt angle α may be recognized by the imaging device 19.
Operations of the conventional component mounting apparatus are now described by referring to FIG. 10. When production operations are started during step #901, a circuit substrate 21 is transported into the apparatus and firmly held by the circuit substrate holder during step #902. Also, a component 3 is picked up from the component supply 2 during step #903. During step #904, a holding condition of the component 3 is detected by the condition sensor 17 at the detecting station 16, and the controller 25 for determining the component holding condition determines whether the component is held in a proper condition or not, based on this detection. If it is determined that the holding condition of the component 3 is within an allowable range for mounting, work flow goes to step #905 during which center 31 of the component 3, or a targeted sucking point, is recognized, and then displacement value Δa (see FIG. 9) between the center 31 of the component 3 and center 32 of the nozzle 14, or a targeted point of the nozzle 14, is measured. Further, tilt angle α (see FIG. 9) of the component 3 is also recognized. If these measurements are made properly during step #906, necessary correction to position and/or angle of the component 3 is made based on the measured displacement value Δa and the tilt angle α. After the circuit substrate 21 is positioned at a proper place of the mounting station 20 during step #907, the component 3 is mounted onto the substrate during step #908. Then, during step #909, it is checked whether this component is a last one to be mounted on that particular circuit substrate or not; in other words, it is checked whether all necessary components 3 are already mounted on that circuit substrate 21 or not. If it is confirmed that all the components were mounted, then, during step #910, it is checked whether this circuit substrate 21 is a final one of a current production lot or not, and if it is confirmed that the circuit substrate 21 is the final one, production operations are completed after the circuit substrate 21 is pulled from the apparatus during step #911.
If it is determined during a detecting operation during step #904 that no component is sucked, a mounting operation is skipped at mounting station 20, and a new component is picked up during step #903 at a next round of index 11 rotation. If it is determined during this component detecting process during step #904 that the component 3 is in an improperly held condition, or the component is a false one, such a component 3 is released into the collecting box 23 at releasing station 22 during step #912, and a new component is picked up during step #903 at a next round of index 11 rotation.
If it is determined, during step #909, that the component 3 just mounted is not the last one to be mounted, or there are still other component(s) to be mounted on the same circuit substrate, the work flow goes back to step #903 for performing subsequent pick up and mounting operations. If it is determined, during step #910, that the circuit substrate is not the final one for the current production lot, the circuit substrate with mounted components is pulled from the apparatus, and a new circuit substrate 21 is fed into the apparatus during step #902. All these operations are repeated until all necessary production operations are completed.